The injection of Manuel Vasquez with a lethal dose of pentobarbital leaves Texas with enough of the powerful sedative to carry out only one more execution.
Vasquez was the fourth Texas inmate put to death this year, and at least six are scheduled for execution in the coming weeks.
Texas prison officials, like those in other death penalty states, have found it increasingly difficult to find suppliers to provide drugs intended for capital punishment use.
Vasquez, in a final statement, told his family and friends he loved them and thanked "the Lord for his kind mercy, faithfulness and unconditional love."
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"In Jesus' name I pray," he said, then told the warden: "I'm ready."
He took three deep breaths and then began snoring loudly. The snores became progressively quiet, and all movement stopped within less than a minute.
The sister of his victim was among witnesses watching through a window. He never looked at her.
His own sister and a female friend cried as they watched through a window in an adjacent room.
Testimony at Vasquez's capital murder trial showed Ybarra had ignored the gang's "dime" tax on street drug sales in San Antonio, so Vasquez and two partners were ordered that she "had to go down."
The men barged into a room at a run-down San Antonio motel where Ybarra was staying with her boyfriend, Moses Bazan. Bazan was beaten and stabbed but survived to identify one of the attackers, leading to the arrest of all three. He also said he saw Vasquez ask one of his companions for a phone cord and saw Vasquez strangling Ybarra.
Court records show the three were carrying out orders from Mexican Mafia boss Rene Munoz, who spent years on the Texas Department of Public Safety's 10 Most Wanted List until his arrest in 2012.